One of the most common problems in effecting communication via a switched telecommunications network is the requirement that the communicating parties in separate locations must be available simultaneously. In order to overcome this difficulty a variety of proposals for call handling have been advanced.
One such arrangement is the Voice Storage system described in the "Bell System Technical Journal", May-June 1982, pages 811-914. One of the services offered by the Voice Storage System is Advanced Calling Service wherein a calling customer may leave a message for a called customer. The calling customer calls a special number to get access to a voice storage system which provides to that voice storage system the voice message, the telephone number of the called customer and an indication of when the voice message is to be delivered. This service has the disadvantage that a calling customer who has just placed a call and found that the called customer is busy forfeits the option of initiating the call and relies on the often unpredictable habits of the called party with respect to retrieval of voice mail messages.
Some of these disadvantages in the mechanics of leaving a message in such a system are overcome in accordance with the teachings of U.S. Pat. No. 4,766,604 which describes a coin telephone comprising a microprocessor. This coin telephone stores the identity of the coin station, the called number, and, if the customer has used a calling card, the number of the calling card. When the calling customer hears a busy tone or recognizes that the called customer does not answer, the calling customer can arrange to have a connection automatically set up to a voice storage system by keying an appropriate access code such as *6. The coin telephone then temporarily disconnects the calling customer, transmits the number of the voice storage system to a connected switching system and, after a connection has been established to the voice storage system, transmits the number of the coin station, the called customer number, and the calling card number. Thus, from the customer's point of view, a connection is automatically set up to a voice storage system as soon as the customer keys the access code. However, such an arrangement requires the use of an expensive telephone instrument and is therefore both expensive and difficult to deploy widely since telephone customers are not likely to purchase such an expensive instrument. The called party's habits in voice mail usage remain a problem.
Another arrangement which permits telephone customers to leave messages via message storage systems is exemplified by the Audix service offered on System 85 Private Branch Exchange (PBX) manufactured by AT&T Technologies. When a calling customer calls someone served by the PBX and that person is busy or does not answer, if that customer keys an appropriate signal, a voice message for the called customer may be recorded for later delivery. This service is limited to destination of the PBX and does not serve the general public.
Other proposed solutions directed to handling PBX switching systems are described in U.S. Pat. Nos. 3,928,729 issued Dec. 23, 1975; 4,809,321 issued Feb. 28, 1989; 4,935,958 issued Jun. 19, 1990; and 4,166,929 issued Sep. 4, 1979. A proposed solution for an ISDN switch is described in U.S. Pat. No. 5,023,868 issued Jun. 11, 1991.
A still different arrangement is proposed in U.S. Pat. No. 4,947,421. That system involves a call waiting arrangement in which a caller is free to exercise discretion in interrupting an on-going telephone call. In this arrangement the caller is prompted by an audible announcement that the called party is busy but that the caller may request interruption of the call by remaining off-hook. If the caller believes that his call is sufficiently important he requests call interruption by remaining off-hook. If the caller chooses not to interrupt, he may make subsequent call attempts promptly because he knows that the called party is busy on another call rather than being away from home. Alternatively the caller may activate an automatic callback arrangement such that a call is completed between the two parties as soon as the status of the called station returns to on-hook.